The Tec family of non-receptor tyrosine kinases plays a central role in signaling through antigen-receptors such as the TCR, BCR and Fcε receptors (reviewed in Miller A, et al. Current Opinion in Immunology 14; 331-340 (2002). Tec family kinases are essential for T cell activation. Three members of the Tec family, Itk, Rlk and Tec, are activated downstream of antigen receptor engagement in T cells and transmit signals to downstream effectors, including PLC-γ. Deletion of Itk in mice results in reduced T cell receptor (TCR)-induced proliferation and secretion of the cytokines IL-2, IL-4, IL-5, IL-10 and IFN-γ. (Schaeffer et al, Science 284; 638-641 (1999)), Fowell et al, Immunity 11; 399-409 (1999), Schaeffer et al Nature Immunology 2, 12; 1183-1188 (2001))). The immunological symptoms of allergic asthma are attenuated in Itk−/− mice. Lung inflammation, eosinophil infiltration and mucous production are drastically reduced in Itk−/− mice in response to challenge with the allergen OVA (Mueller et al, Journal of Immunology 170: 5056-5063 (2003)). Itk has also been implicated in atopic dermatitis. This gene has been reported to be more highly expressed in peripheral blood T cells from patients with moderate and/or severe atopic dermatitis than in controls or patients with mild atopic dermatitis (Matsumoto et al, International archives of Allergy and Immunology 129; 327-340 (2002)).
Tec family kinases are also essential for B cell development and activation. Patients with mutations in Btk have a profound block in B cell development, resulting in the almost complete absence of B lymphocytes and plasma cells, severely reduced Ig levels and a profound inhibition of humoral response to recall antigens (reviewed in Vihinen et al Frontiers in Bioscience 5:d917-928).
Tec kinases also play a role in mast cell activation through the high-affinity IgE receptor (FcεRI). Itk and Btk are expressed in mast cells and are activated by FcεRI cross-linking (Kawakami et al, Journal of Immunology; 3556-3562 (1995)). Btk deficient murine mast cells have reduced degranulation and decreased production of proinflammatory cytokines following FcεRI cross-linking (Kawakami et al. Journal of leukocyte biology 65:286-290). Btk deficiency also results in a decrease of macrophage effector functions (Mukhopadhyay et al, Journal of Immunology; 168, 2914-2921 (2002)).
Accordingly, there is a great need to develop compounds useful as inhibitors of protein kinases. In particular, it would be desirable to develop compounds that are useful as inhibitors of Tec family (e.g., Tec, Btk, Itk/Emt/Tsk, Bmx, Txk/Rlk) protein kinases.